Moonlit Scavengers's ability won't trigger at all if you don't control an artifact or enchantment immediately after it enters the battlefield. If you don't control an artifact or enchantment as the ability resolves, the ability has no effect. These don't have the be the same artifact or enchantment at both times, however.

You still control Auras that you put onto the battlefield attached to a permanent you don't control.

Moonlit Scavengers's ability doesn't return multiple creatures if you control multiple artifacts and/or enchantments.